1. Field of the Invention
The invention relates to nanolithography. More particularly, it relates to a device that maintains a constant tip-surface distance for producing hot nanolithography patterns on a surface using a telescopic nanotube.
2. Description of the Related Art
Nanolithography can be accomplished by mechanically scratching a surface with a sharp atomic force microscope (AFM) tip, by exploiting the electromagnetic enhancement of a laser field in the vicinity of a sharp tip for surface ablation, by using hot tips for thermal imprinting on a surface, or by writing with foreign molecules on a surface. Regardless of the implementation of the particular method for surface modification, two challenges in improving AFM tip nanolithography exist. The first challenge includes achieving high spatial resolutions, which is directly related to the sharpness of the tip. The second challenge includes the accurate control of the tip-surface distance, which affects the nanolithography quality.
AFM hot nanolithography has received particular attention due to its promise to meet the demands of high spatial resolution for surface modification in today's continuous race for miniaturization. Since the imprinting resolution is directly related to the tip sharpness, carbon nanotubes (CNT), with their high aspect ratio, appeared naturally as promising candidates for hot tips. CNT also have the advantage of a more robust chemical and mechanical structure, as compared to the conventional Si tips, which are brittle and can change in size and shape during operation. However, the performance of the nanotube tips when operating in AFM tapping or contact mode is affected by forces which laterally bend the CNT, thus limiting the possibility of producing sharp turns on the surface. At the same time, the AFM conventional non-contact operating mode is rather not suitable for hot nanolithography applications, regardless of the type of tips used, since it involves a mean distance too large for proximity tip-surface heat interactions necessary for thermal imprinting. This is due to the feedback loop that involves large amplitude oscillations of the cantilever at its mechanical resonance frequency. One proposed way to overcome this is based on small amplitude forced oscillations of the cantilever at a frequency different from its resonant frequency, together with a custom feedback circuit. However, such a feedback circuit has to be designed differently for each situation since it is specific to the experimental conditions, such as humidity, sample material, position of the laser spot on the cantilever, etc. . . .
Regarding the task of approaching a surface with a sharp tip and maintaining a constant tip-surface distance, the conventional scheme involves approaching the tip until contact is made with the surface and then raising it to the desired distance. If stiff cantilevers are used, sharp tips are likely to break during the contact with the surface. Conversely, if soft cantilevers are used, the tip may stick to the surface and upon lifting it may jump to a distance larger than the desired one.
Moreover, time efficiency of AFM nanolithography can be problematic. In order to increase it, parallel arrays of Si probes are produced. The advantage of such a parallel operation is the decrease in the scan time for a given image area. Again, the difficulties come from controlling the distance between the sample and the individual tips, since there is only one feedback control for the entire array of cantilevers. The lack of feedback control for the individual tips produces large variation in the nanolithography quality from tip to tip. Therefore, new apparatuses and methods are needed to address these challenges for improved nanolithography applications.